1. Technical Field
This invention relates generally to a method and apparatus for forming a tubular article having a perforated annular wall, and more particularly to a method and an apparatus useful in the manufacture of stents.
2. Background Art
A stent is a relatively new device that supports the walls of weak human arteries. Heretofore, stents have been difficult and costly to fabricate. Typically, stents are formed from tantalum or stainless steel wire that is formed into complex helical shapes. The shapes of commercially available stents require very high levels of plastic deformation of the wire in a die, which work hardens the metal. The formed helical shape is typically maintained by strategically placed, welded joints. The high, localized heating and cooling of the welding process recrystallizes the wire, causing further damage to the wire's material.
Medical stents require flexibility in a bending mode during insertion, as well as torsional and radial stiffness to provide support to the artery wall. Typically, a stent is inserted over an angioplasty balloon and compressed to form a wire mesh sleeve. The balloon and stent sleeve assembly is then inserted into a patient's artery and moved to a desired position. After proper positioning, the balloon is expanded and thereby the stent is permanently enlarged within the artery wall, after which the balloon is withdrawn and the stent retained within the artery. Generally, the stent attaches to the walls of the artery and is exposed to repetitive loading and unloading as it is flexed with the artery walls as a permanent part of a patient's circulatory system.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a stent produced by a method that does not require high deformation rates nor welding, nor other forming processes that would adversely affect the material properties of the stent. It is also desirable to have a method of manufacture for medical stents that does not cause high levels of residual stress in the formed stent. It is also desirable to have the such a method, supported by a suitable apparatus, that is easily automated and controllable.